FIG. 1A illustrates a side elevational view of a prior art sizer 40 used in an extrusion system described in U.S. Pat. No. 6,319,456 to Gilbert et al., entitled “Method for Continuous Vacuum Forming Shaped Polymeric Articles,” issued Nov. 20, 2001, the entirety of which is hereby incorporated by reference. An extruded sheet 10 is subjected to a sizer 40 for mechanical deforming and shaping an extruded sheet. One or more pre-sizers (not shown) may precede the sizer 40. A cross-section of the final sizer is shown in FIG. 1B. This device includes a series of adjustable blocks and plates. The final sizer 40 includes a pair of lateral forming block mechanisms 48 and 52 which can be lever operated for a variety of products and sizes. The final sizer 40 also includes top and bottom forming plates 54 and 56 to maintain the planar nature of the product while the edges are being formed.
Cooling water 42 from the final quench tank 46 is allowed to leak back into the final sizer 40 in order to cool the sheet 10 during sizing. The cooling water 42 quickly quenches the product below its heat deflection temperature to hold its shape. Excess cooling water 42 is removed from the sizer 40 by a vacuum pump 34 and is either removed from the system or recycled back into the quench tank 46.
Following the final sizer operation, the now fully formed extruded sheet 10 is immersed in a quench tank 46 to reduce its temperature to about that of ambient air. The continuous sheet is then removed from the quench tank 46. Following the removal of the product from the quench tank 46, the product can be pulled with the puller machine (not shown) to a cut-off station which severs the now cooled, formed extruded sheet into individual lengths of shaped polymeric articles.
Some prior art sizers additionally include water cavities therein for cooling the steel forming sections. These cavities are isolated from the extruded profile and serve to draw heat dissipated form the extruded profile into the steel shaping sections.
Market and manufacturing pressures are beginning to demand higher out capacities from extrusion processes, and thus sizers, in excess of 3000 lbs/hr of product. While these prior art extruder designs have proved reliable in the past, they have proved ineffective at meeting these increased output demands without sacrificing production quality. Prior art extruders generally require that the product profile cutout within the sizer be oversized at least between about 0.012–0.014 inches with respect to the nominal part thickness of the final cooled product. The sizer's channel must be oversized because it is unable to pull enough heat from the product before the product exits the sizer and is cooled in the quenching tank. The steel sizer also heats up, preventing effective removal of heat from the product. The oversize is necessary to prevent drag between the hot product against the steel sizer. The significant oversize leads to poor dimension control, and ultimately, poor product.
Therefore, there remains a need for a new sizer capable of improving product cooling to allow proper product shaping at higher output rates.